The invention relates to a vibration damper having an amplitude-selective damping device according to the preamble of claim 1.
A vibration damper of this type is known from U.S. Pat. No. 5,248,014. A disadvantage of this known vibration damper is that the amplitude-selective damping device is structurally complex in design. Therefore, the separating piston comprises an annular circumferential groove and radially inwardly directed through-flow channels (shutter passages) which cooperate with through-flow bores (guide passages) in the housing wall defining the space which accommodates the separating piston. Furthermore, in the case of the known vibration damper, the separating piston is supported in both axial displacement directions via springs, so that it is disposed in such a manner as to be non-freely displaceable within the space accommodating it. Therefore, a minimum force which acts hydraulically upon the separating piston is required and this force must be at least greater than the resilient force, acting against it, of the spring which supports the separating piston, in order for the separating piston to be displaced in an axial manner. If the separating piston is displaced in an axial manner, then the periphery of the separating piston cooperates with the through-flow bore which is provided in the wall defining the space which accommodates the separating piston. The bypass volume flow is divided into two partial volume flows, so that not all of the bypass volume is available for the axial displacement of the separating piston. Therefore, in the event of low-amplitude vibration excitations, the pressure acting upon the separating piston can be so low that it is not sufficient for an axial displacement of the separating piston, so that the effect of the amplitude-selective damping device does not arise. In the case of all of the embodiments of an amplitude-selective damping device, in which the separating piston is held in a centred manner by means of springs, the position of the separating piston is dependent upon the differential pressure at the separating piston and not exclusively upon the quantity of damping medium which has flowed in. In such a case, the amplitude-selective function of the damping system is dependent upon speed by reason of the volume flow-pressure interrelationship at the working piston valve.